This invention relates to a liquid heating system which includes a high-pressure hydraulic pump, a pressure-reducing element and a heat exchanger.
A known heating system is disclosed in German published application No. 26 28 697 as including a pump, a pressure-limiting means, and a heating exchanger, liquid medium being fed under pressure by the pump through the pressure-limiting means and being converted into heat for the heating of an intended space. The throttling section of the pressure-limiting means is adjustable in order to be able to control the quantity of heat generated. Thus, the level of heat production is controllable by adjusting the throttling of the pressure-limiting means, although no control is provided for adjusting the discharge rate of the flow produced by the pump.
Such a prior art system has several drawbacks in that adjustable pressure conditions at the pressure side of the pump lead to fluctuating heat production and require continuous adjustments, which can only be controlled with a highly sensitive inertia-less pressure-limiting means.
Moreover, the steady operation of the hydraulic pump and the permanent pressurization of the pressure-limiting means and of the heat exchanger are causes of continuous losses of efficiency and of heat. If the input speed of the pump is not controllable, a considerable flow of heating medium will continue to be recirculated when the heat exchanger requires no calorific heat. Even if, with reduced heat production in the pressure-limiting means, the discharge flow is delivered via a bypass line as a function of the pressure, as provided for by an auxiliary device, the frictional and hydraulic losses will persist.
Control is also inadequate for such a prior art system in the event that a high temperature of the heating medium has already been obtained but no additional heat is required in the space to be heated when it is already sufficiently heated. In such cases, the energy fed by the pump as work and contained in the liquid reservoir as heat is lost without being utilized because of the continuous circulation of the medium through the piping system and through the heat exchanger. Even the auxiliary by-pass line control mentioned above provides less than a suitable remedy of such problem.